1/*
2 * Copyright 2017-present Facebook, Inc.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#pragma once
18
19#include <atomic>
20#include <cstdint>
21
22namespace folly {
23
24/**
25 * Sets a bit at the given index in the binary representation of the integer
26 * to 1. Returns the previous value of the bit, so true if the bit was not
27 * changed, false otherwise
28 *
29 * On some architectures, using this is more efficient than the corresponding
30 * std::atomic::fetch_or() with a mask. For example to set the first (least
31 * significant) bit of an integer, you could do atomic.fetch_or(0b1)
32 *
33 * The efficiency win is only visible in x86 (yet) and comes from the
34 * implementation using the x86 bts instruction when possible.
35 *
36 * When something other than std::atomic is passed, the implementation assumed
37 * incompatibility with this interface and calls Atomic::fetch_or()
38 */
39template <typename Atomic>
40bool atomic_fetch_set(
41 Atomic& atomic,
42 std::size_t bit,
43 std::memory_order order = std::memory_order_seq_cst);
44
45/**
46 * Resets a bit at the given index in the binary representation of the integer
47 * to 0. Returns the previous value of the bit, so true if the bit was
48 * changed, false otherwise
49 *
50 * This follows the same underlying principle and implementation as
51 * fetch_set(). Using the optimized implementation when possible and falling
52 * back to std::atomic::fetch_and() when in debug mode or in an architecture
53 * where an optimization is not possible
54 */
55template <typename Atomic>
56bool atomic_fetch_reset(
57 Atomic& atomic,
58 std::size_t bit,
59 std::memory_order order = std::memory_order_seq_cst);
60
61} // namespace folly
62
63#include <folly/synchronization/AtomicUtil-inl.h>
64